Liquefaction process employing expanded feed as refrigerant



United States Patent 3,377,811 LIQUEFACTION PROCESS EMPLOYIN G EX-PANDED FEED AS REFRIGERANT George W. Siegrist, Coopersburg, and KennethZeitz,

Allentown, Pa., assignors to Air Products and Chemicals, Inc.,Allentown, Pa., a corporation of Delaware Filed Dec. 28, 1965, Ser. No.516,887 2 Claims. (Cl. 6211) ABSTRACT OF THE DISCLOSURE Low temperaturerefrigeration process in which gaseous material is compressed in amulti-st-age compressor to provide intermediate pressure gaseousmaterial and high pressure gaseous material. The intermediate pressurema terial is cooled, expanded with work and then valve expanded toeffect its partial liquefaction, the unliquefied part being used to coolthe intermediate pressure material and then returned to the inlet of thecompressor. The high pressure material is expanded with work and used tocool the intermediate pressure material prior to expansion and thenreturn to the inlet of an intermediate stage of the compressor.

This invention relates to refrigertaion and more particularly to aprocess for producing refrigeration at cryogenic temperatures.

It is an object of the present invention to provide an improved processfor producing refrigeration at cryogenic temperatures.

Another object is to provide a novel low temperature refrigerationprocess which may be used to refrigerate a device to be cooled, toeffect liquefaction of gaseous material, or both.

A further object is to provide an improved low temperature refn'gerationprocess of the foregoing type which is capable by relatively simpleadjustments to meet changes in refrigeration and liquefaction loads.

Still another object of the present invention is to provide a novel lowtemperature refrigeration process which obtains improved efiiciency by anovel use of Joule-Thomson expansion and expansion with production ofexternal work.

Other objects and features of the present invention will become apparentfrom consideration of the following detailed description in connectionwith the accompanying drawing, which is a diagrammatic showing of a lowtemperature refrigeration process according to a preferred embodiment ofthe invention.

Referring to the drawing in greater detail, gaseous material enters theprocess through conduit 10, having a valve 11, from a storage vessel orother sutiable source, not shown, and is conducted to first stage 12 ofa multistage compressor, indicated generally at 14, including secondstage 15 and third stage 17. The compression stages may be of thereciprocating, centrifugal or other suitable type and provided withconventional inter and after coolers, not shown. From the first stage12, gaseous material and recycle gas, to be more fully described later,is conducted by conduit 13 to the second stage 15 and by conduit 16 fromthe second stage to the third stage 17. The compressed gaseous materialfrom the third compression stage is divided at point 18 with a portionbeing conducted 3,377,811 Patented Apr. 16, 1968 by conduit 20 for flowthrough passageway 21 of heat exchange device 22 in countercurrent heatinterchange with relatively cold fluids described below. The compressedgaseous material leaves the cold end of the heat exchange device 22 at alower temperature and is passed by conduit 23 for flow through coil 24in heat interchange with a pool 78 of boiling liquid refrigerant, suchas nitrogen, contained in vesel 25 to effect further cooling of thecompressed gaseous material to a temperature close to the temperature ofthe boiling refrigerant. The cool compressed gaseous material is thenconducted by conduit 26 for flow through passageway 27 of heatexchangedevice 28 in countercurrent heat interchange with relatively coldfluids, described below, to effect further cooling of the gaseousmixture which leaves the cold end of the heat exchange device 28 byconduit 29.

The relatively cold fluids which effect cooling of the compresed gaseousmaterial to the low temperature existing in conduit 29 are derived fromthe liquid refrigerant in vessel 25, an independent refrigeration cycleand relaively cold vapor of the compressed gaseous material, derived ina manner described below, which enters the shell space of heat exchangedevice 28 through conduit 49. Such vapor flows through the shell space50 in countercurrent heat interchange with the compressed gaseousmaterial in passageway 27 and is then conducted by conduit 51 for flowthrough the shell space 52 of the heat exchange device 22 for furthercountercurrent heat interchange with the compressed gaseous material;the vapor leaves the warm end of the heat exchange device 22 at aboutambient temperature and may be merged with the gaseous material enteringthe process through conduit 10.

The refrigeration cycle may be a self-contained, independent systememploying a refrigerant the same as or different from the gaseousmaterial fed to conduit 10, or may embody the compression arrangementdecribed above which is the preferred arrangement when the re frigerantis the same as the gaseous material. As shown, a part of the compressedgaseous material from the third compression stage 17 is used as arefrigerant and fed by conduit 54 to a compressor 55 which may beconsidered the fourth stage of the compressor 14. High pressurerefrigerant from compressor 55 is conducted by conduit 56 for flowthrough pasageway 57 of heat exchange device 58 to cool the highpressure refrigerant upon countercurrent heat interchange withrelatively cold fluids, described below. Cooled high pressurerefrigerant leaves the cold end of heat exchange device 58 by conduit 59and is conducted thereby for flow through coil 60 in heat exchangerelation with the pool 78 of boiling refrigerant contained in the vessel25. The high pressure refrigerant leaves the coil 60 at a temperatureclose to the temperature of the boiling refrigerant and is passed byconduit 61 for flow through passageway 62 of heat exchange de- Vice 63to effect further cooling of the high pressure refrigerant uponcounter-current heat interchange with relatively cold low pressurerefrigerant described below. From the heat exchange device 63, the coldhigh pressure refrigerant is conducted by conduit 64 to the inlet ofexpansion engine 65, of the turbine or reciprocating type, whichfunctions to expand the high pressure refrigerant to a relatively lowsuperatmospheric pressure with production of external work. Theexpansion engine 65 is preferably operated to maintain the efliuentwithin the vapor phase region but close to saturation temperature at therelatively low dischar e pressure. The low pressure refrigerantdischarged from the expansion engine at low temperature is passed byconduit 66 for flow through passageway 67 of heat exchange device 28 incountercurrent heat interchange with relatively warm compressed gaseousmixture flowing through the pasageway 27 of the heat exchange device asdescribed above. The low pressure refrigerant is then employedto coolthe high pressure refrigerant prior t expansion in the engine 65. Asshown, the low pressure refrigerant is conducted by conduit 68 for flowthrough the shell space 69 of heat exchange device 63 and then byconduit 70 for flow through the shell space '71 of heat exchange device58. The low pressure refrigerant leaves the heat exchange device 58 atabout ambient temperature and is conducted by conduit 72 to the inlet ofcompressor stage 15. As mentioned above, the refrigeration cycle maycomprise an independent closed system, in which case the conduit 72would be connected to the inlet of a refrigeration cycle compressor suchas the compressor 55, which may be the multi-stage type, if desired.

The pool 78 of liquid refrigerant, such as nitrogen, colecting in thevessel from the supply conduit 77, is vaporized upon cooling thecompressed gaseous material in coil 24 and the high pressure refrigerantin coil 60, and cold nitrogen vapor is withdrawn from the vessel 25through conduit 79 and utilized to precool the compressed gaseousmixture and the high pressure refrigerant. One part of the cold nitrogenvapor is flowed through passageway S2 of heat exchange device 22 by wayof conduit 80 and another part is passed by conduit 31 for flow throughpassageway 83 of heat exchange device 58. The nitrogen vapor leaves theheat exchange devices 22 and 58 at substantially ambient temperaturethrough conduits 84 and 85, respectively, and is merged in conduit 86and withdrawn from the process.

As mentioned above, one of the objects of the present invention is toprovide a low temperature refrigeration process of improved efficiencyby employing a novel combination of Joule-Thomson expansion andexpansion with production of external work. It has been discovered thata substantial increase in refrigeration produced per unit of inputenergy is obtained by expanding compressed and cooled gaseous mixture intwo stages, first, to a lower, intermediate pressure which may besuperatmospheric pressure or below, by expansion with production ofexternal work and, second, by Joule-Thomson expansion of the gaseousmixture from the intermediate pressure to a lower pressure, whilemaintaining the gaseous material fed to the expansion valve at atemperature as close as possible to the temperature of the gaseousmaterial discharged from the expansion engine. The expansion engine 33is operated under such pressure and temperature conditions to preventliquefaction of the gaseous material. This may be accomplished bymaintaining the temperature of the gaseous mixture fed to the expansionengine above a predetermined value; however, it is preferred, whenpracticing the present invention, to operate the expansion engine underan exhaust pressure slightly greater than the critical pressure of thegaseous mixture to permit cooling of the gaseous mixture fed to theexpansion engine to the lowest possible temperature obtainable from theprocess. Operation of an expansion engine under a discharge pressuregreater than the critical pressure of the material being expandedordinarily does not obtain the refrigeration that, under certaincircumstances, would be produced under lower discharge pressures.However, it has been discovered that the "feature of Joule-Thomsonexpansion of eflluent of an expansion engine, although at a pressuregreater than the critical pressure of the gaseous material beingexpanded, makes it possible to obtain a greater quantity ofrefrigeration per unit of input energy.

With reference to the drawing, cold compressed gaseous mixture from theheat exchange device 28 is conducted by conduit 29 for flow throughpassageway 30 of heat exchange device 31 and thereby further cooled bycounten current heat interchange with relatively cold vapor of thegaseous material, described below. From the heat exchange device 31, thecold compressed gaseous mixture is fed by conduit 32 to the inlet ofexpansion engine 33 which may be of the reciprocating or turbine type.In the expansion engine 33, the gaseous mixture is reduced in pressureto a lower, intermediate pressure with a concomitant reduction intemperature. Preferably, for reasons discussed above, the dischargepressure of the expansion engine is maintained at a superatmosphericpressure slightly greater than the critical pressure of the gaseousmaterial. The gaseous mixture discharged from the expansion engine isfed by conduit 34 directly, i.e., without an intervening heatinterchange step, to an expansion valve 35 wherein the gaseous mixture,at a temperature substantially corresponding to the temperature of theexpander efliuent, undergoes Joule-Thomson expansion to a lower pressurewith a concomitant reduction of temperature to within the liquefactionregion to thereby effect partial liquefaction of the gaseous mixture.The partially liquefied gaseous mixture is fed by conduit 36 to phaseseparator 37 which, in one mode of operation, functions to part thevapor portion from the liquid portion, the liquid portion beingwithdrawn from the phase separator through a valved discharge conduit 38and the vapor portion being withdrawn from the top of the phaseseparator. The vapor portion is passed through valve 39 and conducted byconduit 47 for flow through shell space 48 of heat exchange device 31 tocool the compressed gaseous mixture to the low temperature prior toexpansion in the engine 33. Thereafter, the vapor portion is conductedby conduit 49 for further countercurrent heat interchange with thecompressed gaseous mixture as described above.

In the process shown in the drawing, the components operating under atemperature below the boiling point of the liquid refrigerant in thevessel 25, including expansion engines 33 and 65, phase separator 37,heat exchangers 28, 31 and 63, are located within a chamber defined by aDewar vessel 73 having a vacuum space 74. Heat leakage is minimized by aliquid nitrogen cooled radiation shield shown as a conduit 75 disposedin the vacuum space 74. The liquid nitrogen enters the conduit 75through valve 76 from a suitable source, flows through the conduit 75and exits through conduit 77 which feeds liquid nitrogen to the vessel25.

As mentioned above, one of the objects of the present invention is toprovide a low temperature process that may be used to refrigerate adevice to be cooled, to effect liquefaction of gaseous material, orsimultaneously perform both functions. Liquefied gaseous material may bewithdrawn as product from the phase separator 37 through the dischargeconduit 38, as described above. Also, vapor withdrawn from the phaseseparator 37 or the liquid-vapor mixture fed to the phase separator maybe used to refrigerate a device to be cooled such as device 43 includinga vacuum chamber provided with an internal cool wall represented by acooling coil 44. One end of the cooling coil 44 is connected to thevapor outlet of the phase separator by conduit 42, having a controlvalve 40, and the other end of the coil 44 is connected to the conduit47 by a conduit 46, the latter conduit having a control valve 41 and thevalve 33 being connected between the conduits 42 and 46.

When the process is operated to produce liquid product, the valves 4%)and 41 are closed, valve 39 is open and liquefied gaseous material iswithdrawn from the process through conduit 38. In this mode ofoperation, the total unliquified portion of the gaseous mixture enteringthe phase separator 37 is conducted by conduit 47 for countercurrentheat interchange with the compressed gaseous mixture. In operation ofthe process to utilize the maximum available refrigeration to cool thedevice 43, the

valve 39 is closed, the valved conduit 38 is closed, and valves 40 and41 are open. With such arrangement, the total liquid-vapor mixture fromthe expansion valve 35 flows through the cooling coil 44 where theliquefied portion is vaporized and, when it is desired to maintain thedevice 43 at the lowerest possible temperature, the vapor leaves thecooling coil at saturation temperature and thereafter flows by way ofconduits 46 and 47 for countercurrent heat interchange with thecompressed gaseous mixture. The process is also operable simultaneouslyto produce liquefied product and cool the device 43. In such operation,the valve 39 ordinarily is closed, the valves 40 and 41 are open andliquefied gaseous material is withdrawn through valved conduit 38. Theflow of saturated vapor to the cooling coil 44 through conduit 42 makesit possible to maintain the device 43 at a low temperature above thelowest temperature obtained by the process; however, when it is desiredto maintain the de vice 43 at the lowest possible temperature andsimultaneously produce liquefied gaseous material as product, the phaseseparator 37 may be maintained under a slightly elevated pressurerelative to the pressure of the fluid in the cooling coil 44 byinserting pressure regulating valves in the conduits 38 and 42 and,downstream of such pressure regulating valves, a controlled quantity ofliquefied gaseous material may be transferred from conduit 38 to conduit42 so that saturated vapor leaves the cooling coil 44. Inasmuch as theproduction of liquid product withdraws refrigeration from the process,the relative mass of compressed gaseous material in conduit 20 and highpressure refrigerant in conduit 56 is adjusted by means of controlvalves 90 and 91, respectively, in accordance with the quantity ofliquefied gaseous material withdrawn from the process. When the processis employed solely to cool the device 43, a maximum mass of thecompressed gaseous material flows through conduit 20 and minimumrefrigeration is required by the refrigeration cycle whereas, when theprocess is used solely to produce liquefied gaseous mixture as product,the refrigeration cycle produces maximum refrigeration and a minimummass of compressed gaseous material flows to the expansion engine 33 toobtain the quantity of refrigeration necessary to sustain the process.When the process is employed simultaneously to produce liquid productand cool the device 43, the relative mass of the compressed gaseousmixture and the high pressure refrigerant is adjusted between themaximum and minimum limits depending upon the quantity of liquefiedgaseous material withdrawn as product. Although maximum efliciency ofcomponents of the process, for example, the expansion engines 33 and 65,is obtained when designed for a specific mass flow, the process is socharacterized that high efiiciency is obtained irrespective of the modeof operation by designing the components for operation on the basis of amean mass flow. Of course, when the process is intended primarily for aparticular mode of operation, the components may be designed to obtaingreatest efiiciency when operating according to that mode.

As a specific example, the process provided by the present invention wasperformed employing US. Bureau of Mines Grade A helium as the gaseousmaterial and as the refrigeration medium. About 62% of the heliumdischarged from compressor stage 17 at about 192 p.s.i.a. and 316 K. wasflowed through the heat exchange device 22 and then the coil 24 in heatinterchange with liquid nitrogen in vessel 25 boiling undersubstantially atmospheric pressure to cool the thereby compressed heliumto about 80 K. The compressed helium was further cooled to about 13 K.upon flowing through heat exchange device 28 and then to about 5.5 K.upon flow through the heat exchange device 31, the pressure at thelatter point in the process having dropped to about 182 p.s.i.a. In theexpansion engine 33, the cold helium was reduced in pressure to about 37p.s.i.a. with production of external work and with concomitant coolingto about 5 K. Helium gas at substantially the temperature of 5 K. wasexpanded in valve 35 from about 37 p.s.i.a. to about 17 p.s.i.a with aconcomitant reduction in temperature to about 4.5 K. to form aliquid-vapor mixture of about 70% liquid and 30% vapor. Suchliquid-vapor mixture was passed through conduit 42 to coil 44 to coolthe chamber to about 4.5 K., the chamber being under a vacuum of about 510- torr. The liquefied portion was substantially vaporized in the coil44 and a saturated vapor at about 4.5 K. and 16.5 p.s.i.a. was returnedto the shell side 48 of heat exchange device 31 wherein it was warmed toabout 12 K., further warmed to about 78 K. in heat exchange device 28,then discharged from heat exchange device 22 at about 305 K. andrecycled with the incoming helium feed. The remaining portion of thehelium from the compressor stage 17 was increased to about 450 p.s.i.a.by compressor 55 and, after flowing through heat exchange device 58 andcoil 60, was cooled to about 80 K. The helium refrigerant was furthercooled to about 21 K. in heat exchange device 63, and in the expansionengine 65, the helium refrigerant was reduced in pressure to about 37p.s.i.a. with concomitant cooling to about 12 K. Cold effluent of theexpansion engine 65 was warmed to about 18 K. upon flowing through heatexchange device 28, was further warmed to about 78 K. after flow throughthe heat exchange device 63 and flowed from the heat exchange device 58at about 305 K. and then fed to the inlet of compression stage 15. Whenthe process was operated as a liquefier, the pressure and temperatureconditions corresponded substantially to those given in the foregoingexample; however, about 35% of the compressed helium from thecompression stage 17 was flowed through the process to the expansionengine 33 and the expansion valve 35 with the remainder flowing throughthe refrigeration cycle.

Although the invention has been described in connection with preferredembodiments, it is to be expressly understood that various changes andsubstitutions may be made therein without departing from the spirit ofthe invention as well understood by those skilled in the art. Referencetherefore will be had to the appended claims for a definition of thelimits of the invention.

What is claimed is:

1. A low temperature refrigeration process comprising the steps ofcompressing gaseous material successively in a first compression zone,an intermediate compression zone to provide gaseous material at a firstsuperatmospheric pressure above the critical pressure of the gaseousmaterial and a final compression zone to provide high pressurerefrigerant,

passing gaseous material at the first superatmospheric pressure in heatexchange with relatively cold fluid to cool the gaseous material at saidfirst superatmospheric pressure,

expanding the cool gaseous material at said first superatmosphericpressure with production of external work to a second pressure lowerthan said first superatmospheric pressure with concomitant cooling ofthe gaseous material to a temperature not lower than saturationtemperature of the gaseous material at the second pressure,

further expanding the gaseous material by Joule-Thomson expansion tofurther cool and at least partially liquefy the gaseous material,

utiizing the unliquefied part of the gaseous material to cool thecompressed gaseous material at said first superatmospheric pressure andthereafter feeding the unliquefied part to the inlet of the firstcompression zone,

cooling the high pressure refrigerant and expanding the cooled highpressure refrigerant with production of external work,

passing the work expanded refrigerant in heat interchange with thecompressed gaseous material at said first superatmospheric pressure toaid in cooling the compressed gaseous material prior to its expansion,and then introducing the refrigerant into the inlet of the intermediatecompression zone. 2. A low temperature refrigeration process as definedin claim 1 comprising the further step of controllably adjusting therelative mass of the compressed gaseous material and the refrigerant.

References Cited UNITED STATES PATENTS 2,909,903 10/1959 Zimmermann.

8 4/1960 Mordhorst et a1. 62-9 10/1960 Simonet 62-38 X 5/1963 Becker62-38 X 5/1966 Davis 62-38 X FOREIGN PATENTS 8/ 1965 Great Britain.5/1962 U.S.S.R.

10 NORMAN KUDKOFF, Primary Examiner.

V. W. PRETKA, Assistant Examiner.

